Analog tunable gratings driven by thin-film piezoelectric microelectromechanical actuators.

We present a microfabricated grating whose period can be tuned in analog fashion to within a fraction of a nanometer. The tunable angular range is more than 400 microrad in the first diffracted order. The design concept consists of a diffractive grating defined onto a 400-nm membrane, with the membrane subsequently strained in the direction perpendicular to the grating grooves by thin-film piezoelectric actuation. The strain-tuned grating device was fabricated with microelectromechanical processes, utilizing both surface and bulk micromachining. The fabricated piezoelectric film achieved a measured dielectric constant of 1200. Device characterization yielded grating period changes up to 8.3 nm (0.21% strain in the membrane) at 10 V and a diffracted angular change of 486 microrad, in good agreement with the theory. Uniformity across the actuated grating and out-of-plane deflections are characterized and discussed.